Q&A Hero

Q: An enzymatic reaction has a Vmaxof 30 M/min and a Kmof 50 M. If the concentration of the substrate is 25 M, which of the following is true? a. the velocity will be 7.5 M/min b. the velocity will be 20 M/min c. the velocity will be 10 M/min d. the velocity will be 25 M/min e. the velocity will be 15 M/min

Q: All are characteristics of the enzyme hexokinase EXCEPT: a. It is not highly specific and will catalyze phosphorylation of a number of hexoses at the six position. b. Hexoses bind the active site and induce a solvent inaccessible fit to the hexose. c. Glycerol may fit into the active site, but it does not bind to induce a conformational change necessary for catalysis. d. When a hexose binds the active site, the active site is modified to promote changes in the substrate to a transitional-state intermediate. e. All are true.

Q: Catalytic antibodies, also called ____, are generated against an antigen that is: a. abzymes; an analog of the transition-state intermediate in the reaction. b. abzymes; the substrate of the reaction. c. zymogens; an analog of the product of the reaction. d. holoenzyme; an analog of the transition-state intermediate in the reaction. e. none of the above.

Q: All are characteristics of ribozymes EXCEPT: a. They are critical for removal of introns from mRNA b. They are substrate specific. c. They enhance the reaction rate. d. On the ribosome, they catalyze the peptidyl transferase reaction e. All are true.

Q: All are characteristics of ordered single-displacement reactions EXCEPT: a. Lineweaver-Burk plots with lines that intersect to the left of the 1/v axis. b. a chemically modified enzyme-intermediate. c. the lack of any exchange reaction activity. d. the lack of competitive substrate effects. e. single substrate initial binding activity.

Q: In the glutamate:aspartate aminotransferase catalyzed reaction mechanism, glutamate would react with ____ to form -ketoglutarate. a. E-pyridoxal phosphate complex b. E-pyridoxamine phosphate complex c. aspartate d. oxaloacetate e. none of the above

Q: In the reaction mechanism below, ____ are competitive for binding to free enzyme E. a. P and A b. A and B c. B and Q d. Q and A e. All of the above

Q: In the enzyme catalyzed reaction sequence below, can the E-PO4intermediate be predicted and why? a. Yes, the mechanism is a double-displacement reaction. b. Yes, the reaction fits the ping-pong model. c. No, the reaction is random single-displacement. d. No, the reaction is double-displacement. e. None of the above.

Q: Sildenafil citrate (Viagra) was developed as an inhibitor of: a. acid phosphatases. b. cAMP phosphodiesterases. c. glycogen phosphorylase. d. cGMP phosphodiesterases. e. testosterone reductase.

Q: Penicillin and other -lactam antibiotics form a covalent bond to the enzyme glycoprotein transpeptidase. What type of bond is formed? a. ester b. thioester c. amide d. phosphate e. none of the above

Q: Penicillin is an example of a mechanism-based enzyme inactivator and is a(n): a. competitive inhibitor. b. noncompetitive inhibitor. c. suicide substrate. d. uncompetitive inhibitor. e. none of the above.

Q: In uncompetitive inhibition: a. I combines only with ES. b. I combines only with E. c. I combines with E and ES. d. I combines with EP. e. none of the above.

Q: A plot of 1/V vs. 1/[S] for an enzyme catalyzed reaction gave a line with an equation of y = 0.5x + 0.2. The same enzyme with an inhibitor present gave a line with an equation of y = 1.1x + 0.2. Which of the following statements is true? a. the type of inhibition is competitive b. the type of inhibition is noncompetitive c. the type of inhibition is uncompetitive d. the Vmax with the inhibitor present has decreased e. the Km with the inhibitor present has decreased

Q: Identify the type of reaction that would give the following graph: a. double displacement bisubstrate reaction. b. competitively inhibited reaction. c. single displacement bisubstrate reaction. d. mixed noncompetitively inhibited reaction. e. pure noncompetitively inhibited reaction.

Q: All of the following statements about noncompetitive inhibition are true EXCEPT: a. They interact with the enzyme as well as the enzyme-substrate complex. b. Increasing the concentration of [S] can overcome the inhibition. c. The Vmax value does not remain the same as for a reaction that is not inhibited. d. The inhibitor can cause a conformational change in the enzyme. e. The inhibitor binds to a different site than does the substrate.

Q: Malonate inhibition of succinate dehydrogenase is an example of: a. noncompetitive inhibition. b. competitive inhibition. c. mixed noncompetitive inhibition. d. irreversible inhibition. e. uncompetitive inhibition.

Q: All of the following statements about competitive inhibition are correct EXCEPT: a. Competitive inhibitors are often chemical analogs of the substrate. b. For a group-specific enzyme, one substrate would be a competitive inhibitor of reactions of the other possible substrate. c. Sometimes a product of an enzyme-catalyzed reaction is a competitive inhibitor of its own production. d. In the presence of a competitive inhibitor, the apparent Km would be altered and Vmax would be decreased. e. Competitive inhibitors usually interact with the enzyme at the binding site for a substrate.

Q: All are true for inhibitor I if it is a competitive inhibitor EXCEPT: a. It binds a site other than the active site. b. It is structurally similar to the substrate. c. EI does not give rise to E + P. d. For a given [I], v decreases. e. At some point, S can displace all of I on E.

Q: The pH optimum of an enzyme is: a. always between pH 6-8. b. nearly the same for all enzymes. c. often dependent upon the amino acids that form the active site d. occurs when there is optimum secondary and tertiary structure in the active site of the enzyme. e. both C and D are correct

Q: In transforming the Michaelis-Menten equation into a straight line equation, y = mx + b, the Lineweaver-Burk double reciprocal plot, which of the following is NOT a true representation? a. slope = Km/Vmax b. y-intercept is 1/Vmax c. x-intercept is 1/Km d. y = 1/V e. x = 1/[S]

Q: The International Units of an enzyme are based on the: a. ratio of enzyme to other proteins. b. micromoles of product formed per minute. c. moles of substrate reacted. d. micromoles of product produced at Vmax/2. e. none of the above.

Q: Which of the following statements is NOT characteristic of kcat/Km?a. It corresponds to a second-order rate constant.b. It provides an excellent parameter for comparison of the catalytic efficiency of enzymes.c. It reflects the property of the enzyme when substrate concentration is at saturation.d. The upper limit for the kcat/Km value is fixed by the diffusion-controlled limit for reactions, which is 109 M-­1 s-­1.e. It is also referred to as the turnover number.

Q: All are true for kcatEXCEPT : a. referred to as the molecular activity of the enzyme. b. called the turnover number of the enzyme. c. measures the maximal catalytic activity or kinetic efficiency of an enzyme. d. defines the number of substrate molecules converted into product/enzyme molecule/unit of time when the enzyme is saturated with substrate. e. all are true.

Q: For an enzyme-catalyzed reaction, the initial velocity was determined at two different concentrations of the substrate. Which of the following would be closest to the value of Vmax? [S] (mM) Vo(mM/min) 1.0 2.0 4.0 2.8 a. 4.7 mM/min b. 0.67 mM/min c. 3.19 mM/min d. 1.5 mM/min e. 0.32 mM/min

Q: For an enzyme-catalyzed reaction, the initial velocity was determined at two different concentrations of the substrate. Which of the following would be closest to the value of Km? [S] (mM) Vo(mM/min) 1.0 2.0 4.0 2.8 a. 0.17 mM b. 5.7 mM c. 2.7 mM d. 0.60 mM e. 1.7 mM

Q: If an enzyme has a Vmaxof 15 mM/min, what is the velocity if the substrate is present at 1/5 of the Km? a. 12 mM/min b. 6 mM/min c. 3 mM/min d. 2.5 mM/min e. cannot be determined from given information

Q: All of the following statements are true about the relationships between [S], Kmand VmaxEXCEPT: a. As the [S] is increased, v approaches the limiting value, Vmax. b. Km = Vmax/2. c. The rate of the reaction, v, follows a first order rate equation v = K'[A] and K' = Vmax/Km. d. The rate of product formed, v, is at Vmax when [S] >> Km. e. Km and Vmax assist in finding the rate of the enzyme catalyzed reaction only if the reaction is irreversible.

Q: Which statement is correct about the Michaelis-Menten constant, Km, for the kinetic mechanism below?a. It is numerically equal to the substrate concentration required to achieve one half the maximum velocity.b. Its defined as Km = k1/(k-­1 + k2).c. It is approximately equal to the dissociation constant for the enzyme-substrate complex to E + P.d. The value of Km is constant for an enzyme regardless of the specific substrate molecule used to determine it.e. Its numeric value has the units of moles-­1.

Q: Which of the following is true regarding the Briggs and Haldane steady state assumption? a. It is defined by the equation b. It states the rate of enzyme-substrate complex formation differs from the rate of enzyme-substrate disappearance. c. The concentration of the enzyme-substrate complex reaches a constant value even in a dynamic system. d. The enzyme-substrate complex will always dissociate to form E + P. e. The total amount of enzyme is variable, depending on the amount of substrate available.

Q: When every enzyme molecule in the reaction mixture has its substrate-binding site occupied by substrate, the kinetics become ____-order, and the velocity is ____. a. zero; Vmax b. first; Vmax c. second; Vmax/2 d. zero; Vmax/2 e. first; Vmax/2

Q: All are true for catalysts EXCEPT: a. They work by lowering the energy of activation. b. The average energy of the reaction is unchanged. c. They combine transiently with the reactants promoting a reactive transition state condition. d. They are regenerated after each reaction cycle. e. All are true.

Q: How do catalysts work to accelerate a chemical reaction? a. They raise the average energy of the reactants. b. They provide a means of acceleration by being completely consumed in the reaction. c. They lower the energy of activation. d. They lower the overall free energy change of the reaction. e. They raise the overall free energy change of the reaction.

Q: All of the following are true statements about the transition state of a reaction EXCEPT: a. The transition state is not an appropriate indication of the rate of a reaction. b. The transition state is located at the height of a free energy diagram. c. The energy required to raise the average energy of one mole of reactant to the transition state is the free energy of activation. d. Reaching the transition state indicates that there is a high probability that the reaction will occur. e. The transition state energy level is the sum of the energy levels of the reactants and products.

Q: The free energy of activation, G, is defined as:a. The average free energy of the product formed.b. The rate of a chemical reaction in relationship to the concentration of reactant molecules.c. The energy required to raise the average energy of one mole of reactant to the transition state energy.d. The amount of energy released by a spontaneous reaction.e. The lowest point on a free energy diagram.

Q: What reaction would NOT proceed via bimolecular elementary steps?a. C + D -> T + Ub. A reaction with a rate constant in the units of s-­1.c. 2A -> D + Ed. A reaction with a molecularity of 2.e. A reaction with a rate constant in the units of M-1s-­1.

Q: The catalytically active complex of an apoenzyme and its prosthetic group is referred to a(n) ____. a. catalytic duo b. holoenzyme c. prosthetic enzyme d. dimeric enzyme e. none of the above

Q: All of the following are properties of a coenzyme EXCEPT: a. They are usually actively involved in the catalytic reaction of the enzyme. b. They tend to be stable to heat. c. They can serve as intermediate carriers of functional groups. d. They are protein components. e. They may contain vitamins as part of their structure.

Q: The trivial term for an enzyme that moves a functional group from one place to another on the substrate is ___________, a. isomerase b. oxidoreductase c. protease d. kinase e. catalase

Q: The specific site on the enzyme where ____ binds and catalysis occurs is called the ____ site. a. coenzyme; substrate b. substrate; active c. coenzyme; regulatory d. regulatory; active e. none of the above

Q: An enzyme's specificity can be due to: a. the ratio of catalyzed rate to the uncatalyzed rate of reaction. b. molecular recognition based on structural complementarity. c. amount of enzyme produced by the cell. d. amount of substrate available. e. metabolic activators.

Q: If the rate constant for the enzyme catalyzed reaction is 2 ï‚´105/sec and the rate constant for the uncatalyzed reaction is 2 ï‚´106/sec, the catalytic power of the enzyme is:a. 1011b. 2 x 10-11c. 10­-11d. 10-1e. 2 x 10-1

Q: Which of the following statements is true regarding enzyme pathways? a. the most effective way to control a pathway is to regulate every enzyme in the pathway b. an enzyme pathway always proceeds in only one direction, never in reverse c. a regulatory enzyme is regulated only by molecules within the given pathway d. metabolic pathways are necessary since enzymes usually catalyze only one specific reaction e. none of the above are true

Q: Enzymes work by:a. providing an alternate reaction pathwayb. increasing the spontaneity (G) of the reactionc. lowering the activation energy of the reactiond. altering the concentration of the reactants to achieve a favorable Ge. proceeding in only one direction, from reactants to products

Q: All are distinctive features of enzymes EXCEPT:a. regulation.b. catalytic activity.c. ability to change G.d. specificity.e. none is true.

Q: Which of the following describes the major utility of a eukaryotic cDNA library if one is trying to express a protein present in a eukaryotic cell? a. the library represents all genes that were actively expressed at a specific time b. the genes lack introns and thus can be expressed by bacterial expression systems c. cDNA libraries are readily available d. all of the above are correct e. both A and B are correct

Q: In a DNA microarray, how many different oligonucleotides can be produced if each oligonucleotide is 20 nucleotides long? a. 420 b. 204 c. 80 d. 20 e. none of the above

Q: The original development of PCR did not use the Taq polymerase. What is the reason that the Taq polymerase is currently used? a. the DNA melting step at 95C would cause denaturation of most DNA polymerases from other organisms b. the Taq polymerase is one of the most rapid DNA polymerase enzymes known and is therefore extremely useful for PCR c. the original method of PCR required that DNA polymerase be added prior to each round of elongation, something that is not conducive to automation d. the Taq polymerase is the only DNA polymerase that will allow production of 2n amounts of DNA (where n=number of cycles) e. both A and C are corect

Q: All are strategies for human gene therapy EXCEPT: a. use of expression cassettes. b. incorporation into expression vectors. c. transfer into patient cells. d. introduction of transformed stem cells. e. all are true.

Q: The most promising vector for human gene therapy is ____.a. yeastb. E colic. human papilloma virusd. adenoviruse. bacteriophage

Q: How does RNA interference function? a. siRNA binds to genes and prevents transcription b. a single strand of the siRNA binds to the gene transcript, preventing translation c. the double stranded siRNA binds to mRNA to prevent ribosomal association d. siRNA binds to RNA polymerase preventing mRNA production e. none of the above

Q: PCR-based mutagenesis is used to create: a. mutant strains of an eukaryotic organism. b. generally modified plasmid vectors. c. mutant bacterial strains. d. mutant DNA libraries. e. specifically altered proteins.

Q: What would be the 9-residue primer used to amplify: 5'-ATCGACGTTACGCTACATAGCATAAGGCTT-3' a. 5'-TAGCTGCAA-3' b. 5'-AAGCCTTAT-3' c. 5'-UAGCUGCAA-3' d. 5'-AAGCCUUAU-3' e. 5'-TGCGATGTA-3'

Q: Which of the following is the appropriate source of the DNA polymerase included in the PCR reaction mixture? a. E. coli b. bacteriophage T4 c. Thermus aquaticus d. Drosophila melanogaster e. Human

Q: In vitro____ makes it possible to alter the nucleotide sequence of a cloned gene systematically. a. protein synthesis b. mRNA synthesis c. hybridization d. mutagenesis e. all are true

Q: RT-PCR differs from basic PCR in that: a. reverse temperatures are used for annealing and transcription. b. transcription is reversed from 5' to 3' ends. c. reverse transcriptase is used to synthesize a cDNA strand complementary to an RNA strand. d. reverse transcripase is used to synthesize an RNA strand from the DNA strand. e. none of the above.

Q: Each cycle of amplification in PCR involves all of the steps EXCEPT: a. the addition of fresh dNTPs to the reaction mixture. b. annealing of oligodeoxyribonucleotide primers to DNA. c. thermal denaturation of the target duplex DNA. d. reaction with DNA polymerase at approximately 70ï‚°C. e. none of the above.

Q: Reporter genes such as those for green fluorescent protein (GFP) are found on many commercial plasmids. These genes are useful to determine: a. if the plasmid is in the host. b. if a gene is present in a library. c. if a foreign protein is being expressed on a vector. d. the relative strength of a promoter sequence. e. all of the above.

Q: Hybrid proteins or fusion proteins are produced by: a. incubation of two proteins with a protease. b. expression of genes coding for multiple proteins. c. translation of mRNAs without removing exons. d. translation of recombinant sequences from expression vectors carrying cDNA inserts cloned directly into the coding sequence of a vector-born protein-coding gene. e. all of the above.

Q: To express a eukaryotic protein in E. coli, the eukaryotic cDNA must be cloned in a(n) ____ that contains ____ and ____. a. expression vector; promoter; ribosomal-binding site b. hybridization complex; promoter; transition start site c. mRNA; ribosomal-binding site; promoter d. mRNA; introns; exons e. none of the above

Q: The study of all of the proteins expressed by a certain cell or tissue under specific conditions is called: a. genetics. b. proteomics. c. embryogenesis. d. mutagenesis. e. all of the above.

Q: Looking at all of the genes that are activated during a major metabolic shift or during embryogenesis and development of organisms is called: a. fractional expression. b. genetic fractionation. c. functional genomics. d. mutagenesis. e. none of the above.

Q: The correct sequence of procedures in the Southern blotting (hybridization) technique is: A. hybridization with radioactive probe. B. agarose gel electrophoresis and visualize bands. C. transfer (blot) to nitrocellulose filter. D. digest DNA with restriction nucleases. E. expose filter to X-ray film, develop and observe. a. B, A, C, E, D b. D, C, B, A, E c. C, D, B, E, A d. D, B, C, A, E e. A, B, C, D, E

Q: All are true for cDNA libraries EXCEPT: a. reverse transcriptase synthesizes a DNA strand complement of the mRNA templates. b. mRNA templates are isolated using oligo (dA)-cellulose chromatography. c. linkers are added and the cDNA is cloned into suitable vectors. d. the cDNA are copies from mRNA templates. e. all are true.

Q: In the Southern hybridization procedure, the gel after electrophoresis is treated with NaOH and then neutralized before blotting. What is the primary function of the alkaline treatment? a. It neutralizes any acid soluble impurities in the gel. b. It cleaves the DNA into smaller fragments to permit greater efficiency of transfer. c. It inactivates any restriction endonucleases that may be in the gel. d. It neutralizes any acidic phosphate groups that might prevent hybridization. e. It denatures the duplex DNA to single-stranded DNA (ssDNA).

Q: The correct sequence for colony hybridization experiments is: A. A replica of the bacterial colonies is obtained on an absorbent disc. B. Autoradiography of the disc reveals probe complementary DNA. C. Host bacteria with plasmid are plated and allowed to grow overnight. D. The disc is treated with alkali. E. The disc is reacted with labeled probe. a. A, C, E, B, D b. C, A, E, D, B c. C, E, A, B, D d. C, A, E, B, D e. C, A, D, E, B

Q: A genomic DNA library is: a. a collection of short fragments from nuclear DNA digestion. b. arrays of synthetic oligonucleotides used to select for a specific DNA. c. a set of cloned fragments that collectively represent the genes of a particular organism. d. a short segment of DNA whose sequence is complementary to a portion of the DNA of interest. e. a circular DNA molecule of 1 kb to 200 kb found in bacteria and yeast cells.

Q: All are characteristic of YACs (yeast artificial chromosomes) EXCEPT: a. YACs can successfully propagate DNA molecules of 2 megabase pairs in length. b. YACs have been transferred into animals. c. YACs must include a centromere. d. YACs must include telomers. e. All are true.

Q: Shuttle vectors have the property that they: a. contain promoters for the expression of the gene. b. have origins of replication for two different cell types, usually bacteria and yeast. c. are capable of incorporating very large DNA fragments. d. contain more than one antibiotic resistant gene. e. none of the above

Q: The advantages of using the pET plasmid system include ____. a. genes to be expressed are under the control of a T7 promoter b. the T7 polymerase is slower than a typical E coli polymerase c. the expressed protein never accounts for more than 5% of the total cell protein d. the T7 polymerase is under the control of the lac operon and is thus only active when induced by an agent such as IPTG e. both a and d are correct

Q: One of the problems with plasmids like pUR278 is that there is no true marker for determining whether or not the plasmid contains the inserted gene since the cloning site does not lie within any specific gene. Which of the following would be an extremely useful tool for rapid selection of those bacteria that have taken up a plasmid with the desired DNA insert? a. look for the production of the lacZ gene by adding X-gal to the growth medium b. include the gene for a fluorescent protein such as GFP in the inserted DNA c. after ligating the DNA insert and plasmid, separate the mixture of DNA molecules by agarose gel electrophoresis to isolate the DNA molecule that corresponds to the size of the plasmid+insert d. look for ampicillin resistance in the transformed cells e. none of the above would be effective

Q: All are steps in the sequence for construction of a chimeric plasmid EXCEPT: a. annealing the ends of the vector and foreign DNA. b. cutting the source of the foreign DNA with a restriction endonuclease. c. reannealing the ends of the vector back together. d. cutting the vector plasmid with the same restriction endonuclease. e. none of the above.

Q: If DNA fragments of about 4 kb are to be cloned, which vector would be most useful? a. plasmid b. cosmid c. YACs (yeast artificial chromosomes) d. bacteriophage lambda e. E. coli chromosome

Q: A method used to insert or transform cells with a plasmid is to:a. add the DNA to bacterial cells that have been lightly treated with lysozyme to produce "holes" in the cell wall.b. add the DNA to a heated suspension of cells at 42°C.c. treat the bacteria with Ca2+, add the DNA, and briefly heat to 42°C.d. incubate the DNA with the cells overnight at 4°C.e. mixing plasmids with an extract of broken cells.

Q: To position a gene in an expression vector downstream from a promoter (i.e., perform directional cloning), it is best to: a. use the largest plasmid available. b. treat the gene with DNase I. c. restrict both the gene and the plasmid with one restriction endonuclease and then screen all colonies for those that express the gene. d. restrict each end of the DNA fragment (gene) with a different restriction endonuclease and do likewise for the plasmid. e. use a vector with two sites for the same restriction endonuclease.

Q: If the pBR322 were treated with PstI in order to insert a gene into the plasmid, which of the following would be correct regarding cells that were transformed with the resulting vector? a. cells that contained the desired vector would be resistant to ampicillin but sensitive to tetracycline b. cells that contained the desired vector would be resistant to tetracycline but sensitive to ampicillin c. cells that contained the desired vector would be resistant to both ampicillin and tetracycline d. cells that contained the desired vector would be sensitive to both ampicillin and tetracycline e. none of the above

Q: All are features of a plasmid useful for cloning EXCEPT: a. expressed sequence tag. b. a cloning site. c. a replicator (origin of replication). d. a selectable marker. e. all are features.

Q: All are characteristic of plasmids EXCEPT: a. naturally occurring, circular extrachromosomal DNA. b. able to perpetuate themselves without a host organism. c. artificial plasmids can be constructed by restriction endonuclease digestion, insertion, and ligation. d. harbor genes for novel metabolic activities. e. an origin of replication must be included in the plasmid to facilitate propagation.

Q: The dimethoxytrityl (DMTr) group protects which functional group during synthetic DNA synthesis? a. the primary amine group of adenine and guanine b. the primary amine group of cytosine c. the 3' hydroxyl of the deoxyribose d. the 5' hydroxyl of the deoxyribose e. both A and B are correct

Q: Which of the following histone proteins has only one copy per nucleosome? a. H1 b. H2A c. H2B d. H3 e. H4

Q: Phylogenetic comparisons of secondary structures of rRNAs from a variety of species revels ____ structures and ____ nucleotide sequences of the rRNAs themselves. a. strikingly similar; high degree of similarity b. strikingly similar; low degree of similarity c. dissimilar; high degree of similarity d. dissimilar; low degree of similarity e. none of the above